1. Field of the Invention
The present invention relates to a device for calculating an estimated acceleration and speed of a vehicle as required for use in the wheel behavior control, such as an antilock brake control, and, more particularly, to a device for calculating the estimated acceleration and speed of a vehicle based on the wheel speed and the output of a gravity-type accelerometer.
2. Description of the Prior Art
In antilock brake control devices and other wheel behavior control devices, estimating the vehicle speed based on calculation of wheel slipping or spinning, and estimating the coefficient of friction between the tire and the road surface are important factors directly affecting the control performance of the device. Estimating the coefficient of friction between the tire and road is normally based on the estimated value of vehicle acceleration during control, and the estimated vehicle acceleration is calculated based on the estimated vehicle speed. Therefore, the performance of the wheel behavior control device is greatly dependent upon the precision of vehicle speed estimation.
However, if the vehicle speed is estimated from the wheel speed alone, the precision of the estimation would be reduced significantly when the tires slip or spin badly.
Therefore, if the estimated vehicle speed and estimated vehicle acceleration are obtained based on both the wheel speed and the acceleration obtained from a reliable accelerometer, the estimating precision can be significantly improved. A typical type of accelerometer is the gravity-type accelerometer.
However, as illustrated in FIG. 3, the gravity-type accelerometer detects acceleration by converting the displacement of a weight F caused by acceleration to an electrical signal using resistors, piezoelectric elements, differential transformers, and other devices.
Therefore, it may be preferable to use the estimated vehicle speed based on the wheel speed when the wheels are not in a state of excessive slipping or spinning, and to use the estimated vehicle speed based on the gravity-type accelerometer when the wheels are in a state of excessive slipping or spinning.
Following this line of reasoning in the design of a wheel behavior control system, at a moment when the determination is made that, excessive slipping or spinning has occurred or has ceased, it is necessary that the estimated vehicle speed obtained from the wheel speed and the estimated vehicle speed obtained from the gravity-type accelerometer be equal, and it is desirable that the estimated vehicle acceleration obtained from the wheel speed and the estimated vehicle acceleration obtained from the gravity-type accelerometer also be equal.
To satisfy these requirements, the problem is how to configure a means for calculating the estimated vehicle speed based on the wheel speed, a means for calculating the estimated vehicle speed based on the output of the corrected gravity-type accelerometer, and a means for determining when to switch from the former estimated vehicle speed to the latter estimated vehicle speed and when to switch back.
Further problems to be solved are how to configure the device so that, when the estimated vehicle speed is obtained, the estimated vehicle acceleration can also be obtained at the same time using the simplest possible operation, and how to control the degree of dependency on the gravity-type accelerometer according to the degree of the tire slipping or spinning.